For the assembler it has to be
ASMPro, and then get AGAguide.lha from Aminet too.
If you can find some old issues of LSD's Grapevine Disk mag then Rombust's coding tutorials were good there are also some good sources and tutorials at the
AmyCoders home page. There is also a coding forum at
ADA which is very useful for beginners.
Assuming you're doing direct-to-hardware coding, you'll need some code to cleanly kill the system, store all important registers and then restore everything then your program/demo quits (these days people are really picky if they run your intro, and then their Workbench hangs when they quit). Try
this code from Share and Enjoy (part of the
How to Code series from Jolyon Ralph).
